Cracks Off Eastern Seabed May Cause Tsunamis, Experts Say

By WILLIAM J. BROAD

Published: May 3, 2000

In waters off Virginia and North Carolina, scientists have found cracks in the seabed that might set off a tsunami, they say, sending waves as high as 20 feet speeding toward the Middle Atlantic states.

Dr. Neal W. Driscoll of the Woods Hole Oceanographic Institute, Jeffrey K. Weissel of Columbia University and John A. Goff of the University of Texas said in their article in the May issue of the journal Geology that the recently discovered cracks could mean the continental shelf was unstable and could slide down like an avalanche, inducing the giant waves.

The scientists said they discovered the cracks about 60 miles from shore along a 25-mile section of the continental shelf off the Virginia and North Carolina coasts. If the seabed there gives way, they said, the reaction could set off the giant waves.

''From a societal perspective, we need to evaluate the degree of tsunami hazard that might be posed by a major submarine landslide,'' the scientists wrote. And they plan to find out if the cracks ''are fossil features or are active and likely to produce a potentially disastrous, large submarine slide in the near future.''

The scientists are leaving this weekend on a 14-day expedition to gather more data to assess the risk.

''We don't want to sensationalize this,'' Dr. Driscoll said in an interview. ''The risk associated with these cracks is finite.''

The long fissures were found 325 to 650 feet beneath the waves and lie perched close to the edge of the outer continental shelf.

If the danger of the cracks proves real, the scientists said, coastal areas of North Carolina, southern Virginia and the lower Chesapeake Bay would be at risk for wave heights similar to the surge of a Category 4 hurricane, which is characterized by top sustained winds of 131 to 155 miles per hour.

The scientists plan to make sonar images of the cracks, and then take deep samples of the seabed to see if the cracks are fresh or covered with layers of sediment. The latter finding would suggest that the cracks were geologically inactive and a low threat of producing giant waves.